The vapor phase polymerization of olefin using a fluidized bed apparatus as well known. For example, according to the disclosure in Japanese Laid-Open Patent Publication No. 47-13962, the following items are referred to as main factors in the fluidized bed vapor phase polymerization apparatus:
(I) to form a fluidized bed with polymer particles,
(II) to provide even distribution of olefin gas with a gas distribution plate,
(III) to fluidize the particles and remove the heat of polymerization with an olefin gas,
(IV) to cool a reactor with the circulation of a olefin gas using an external heat exchanger,
(V) to feed a solid catalyst into the reactor chamber,
(VI) to feed a catalyst promoter, and
(VII) to control the height of the fluidized bed and to remove polymer particles from the reaction chamber.
In addition, a vapor phase polymerization apparatus utilizing a stirred bed reactor is also well known (e.g., Japanese Patent Publication No. 59-21321).
When any type of the above-mentioned polymerization apparatus is used, the controlling of polymerization reaction is an important factor in practical operation. This is usually done by regulating the rate of feeding of a catalyst. However, the conventional olefin polymerization process is carried out under a pressure higher than ordinary pressure and the conventional catalyst employed is in the form of powder. It is difficult, in the conventional practice to continually feed predetermined quantities of solid catalyst powder in small doses.
In order to solve the above problem, Japanese Patent Publication No. 49-17426, discloses a method by which is a catalyst is fed into a fluidized bed reactor through four steps of subdividing, intercepting, exposing and flashing the catalyst by the combination of alternatively opening and closing of a catalyst feed line. Furthermore, catalyst feeding apparatus substantially based on the above method are disclosed in Japanese Patent Publication Nos. 52-45750 and 53-8666.
When a highly active catalyst in a lumpy state is fed into a reactor, polymerization is initiated before catalyst particles become well dispersed. This is not desirable because the polymer particles that are melted by the heat of polymerization are liable to gather into lumps. The highly active catalysts developed in recent years are liable to cause problems of this kind. Accordingly, a process to feed a catalyst in a lump form must be avoided if possible. It is preferable that a weighed catalyst be fed continually in small doses. In such a case, however, when the amount of each feed is too small, even though the formation of lumps is reduced, the number of complicated valve operation to regulate a catalyst feed increases, undesirably increasing the number of man-hours. In other words, in industrial operations, it is required that each dose of a catalyst is large to some extent.
In view of the above-described requirement, the object of the present invention is to provide a process for continually feeding a catalyst in small doses in a dispersed state without difficulty in a vapor phase polymerization process employing a fluidized bed reactor.